Logo (programming language): Difference between revisions

Revision as of 09:16, 1 December 2003

Revision as of 23:49, 7 December 2003

Line 1:

[[fr:Logo]][[pl:J%EAzyk programowania Logo]] [[zh:Logo程序设计语言]]

Logo was

'''Logo''' is a computer [[programming language]] designed by [[Seymour Papert]] in the late [[1960s]] to teach computer skills to children. Papert is a professor at [[MIT]], and the author of ''Mindstorms: Children, Computers, and Powerful Ideas''. Logo is from the Greek word "logos" meaning "word".

Papert

later added the "turtle graphics" for which Logo is now most famous.

'''Logo''' is a computer [[programming language]] designedfirst by [[Seymour Papert]]developed in the late [[1960s]], toby teacha computerteam skillsat toBBN children.led Papert is a professor atby [[MITSeymour Papert]], Wallace Feurzeig, and theDaniel authorBobrow. ofLogo ''Mindstorms:was Children,originally Computers,about manipulating words and Powerfulsentences, Ideas''.hence its Logoname, isderived from the Greek word "logos" meaning "word".

Papert used [[Lisp programming language|LISP]] but changed the [[syntax]] so it is much easier to read. One could say that Logo is Lisp without the parentheses. Today, it is known principally for its "Turtle Graphics" but it has significant list handling facilities, file handling and I/O facilities and can be used to teach most computer science concepts, as Brian Harvey does in his "Computer Science Logo Style" trilogy. Equally it can be used to prepare [[microworlds]] for students to investigate.

Papert who is a professor at [[MIT]], and the author of ''Mindstorms: Children, Computers, and Powerful Ideas'',later added the turtle graphics for which Logo is now most famous.

Papert used [[Lisp programming language|LISP]] but changed the [[syntax]] so it is much easier to read. One could say that Logo is Lisp without the parentheses. Today, it is known principally for its "Turtle Graphics" but it has significant list handling facilities, file handling and I/O facilities and can be used to teach most computer science concepts, as Brian Harvey does in his "Computer Science Logo Style" trilogy. Equally it can be used to prepare [[microworlds]] for students to investigate.,

There are over 130 implementations of Logo- each having their own strengths. A popular Linux implementation is UCBLogo and MSWLogo its freeware Windows derivative is commonly used in UK schools, Comenius Logo is available in Dutch, German, Czech et c. and is worth considering.

==Logo Programming==

The idea is that a turtle with a pen strapped to it couldcan be instructed to do simple things like move forward 100 spaces or turn around. From these building blocks you couldcan build more complex shapes like squares, triangles, circles--using these to draw houses or sail boats.

The turtle movedmoves with commands that wereare relative to its own position, "LEFT 90" meant rotate left by 90 degrees. A student could understand (and predict and reason about) the turtle's motion by imagining what she would do if she were the turtle. Papert called this "body syntonic" reasoning.

The idea of turtle graphics is also useful for

Line 65 ⟶ 70:

====Example 5: New words====

You can teach the turtle new words, i.e. groups of instructions,or procedures. These can to be done from theLogo prompt or an Editor, that wasis knowninvoked asby <cite>EDALL</cite>. Thisin maymany vary with otherlogo dialects. of LOGO. <br> 'TO CHAIR' must be on a separate line. 'END' must be on a separate line. Anything written after a ';' is ignored- so can be used as a comment.

Line 76 ⟶ 81:

</code>

If you are using the editor you must exit from it, and the new word is saved into the avalabeavailabe vocabulary, but will be loostlost when LOGO is exited.

Now any time <code>CHAIR</code> is entered, "<code>REPEAT 4 [FD 100 LEFT 90] FD 30</code>" will be executed. You could compound these by <code>REPEAT 4 [CHAIR] if you wanted.</code>

====Example 6: Erasing (In the UCBLogo dialect)====

The turtle can erase a line. <code>PENERASE PE</code>. You must then replace the 'pen' with the command <code>PENPAINT PPT</code>.

Line 91 ⟶ 96:

END

</code>

====Example 7: Parameters- giving the word changeable information ====

Line 108 ⟶ 114:

==The Language==

Logo is an interpreted language. It is not case dependant , but retains the case used for formatting. It is written in lines . It is a compromise between a sequential programming language with block structures, and a functional programming language. There is no 'standard' LOGO, but UCBLogo is highly regarded. It is a teaching language but its list handling facilities make it remarkable useful for producing useful scripts.

===Functions/Procedures===

Line 142 ⟶ 148:

===Data===

There are three datatypes in UCBLogo,

* the word,

Line 186 ⟶ 192:

* Recursion rather than iteration is the natural method to process lists.

====Example 9: Using List primitiveprimitives to extract the first 5 members of a list====

a: One way would be to use iteration.

to first5firstfive :alist

ifelse lessp count :alist 5 [ op :alist ][

make "olist []

repeat 5 [ make "olist lput first :alist :olist make "alist bf :alist ] opoutput :olist ]

end

show first5firstfive [1 2 3 4 5 6 7 8 9 ]

[1 2 3 4 5]

foreach first5firstfive [1 2 3 4 5 6 7 8 9 ] show 10 - ?

[9 8 7 6 5]

b: Another, more elegant way would be

to firstn :num :list

if :num = 0 [output []]

output fput (first :list) (firstn :num-1 butfirst :list)

end

to firstfive :list

output firstn 5 :list

end

This method uses recursion, and is an example of a 'functional' rather than a 'sequential' programming approach.

===Control Structure Commands===